1. Field of the Invention
The present invention relates to a vehicle body panel structure which can reduce summer heat and provide a comfortable thermal environment. Specifically, the present invention relates to a vehicle body panel structure which is provided with both functions of insulation and dissipation of heat to allow interception of incoming heat from the outside and promotion of dissipation of heat from a cabin interior for the purposes of reduction in atmospheric temperature in the cabin and reduction of the temperature of the vehicle interior parts when a vehicle is parked in blazing sunshine.
2. Description of the Related Art
Temperature inside a cabin of a vehicle placed in blazing sunshine becomes very high. In a measurement example of a summer environment in Japan, the cabin's air temperature reaches nearly 70° C. in the case of a parked vehicle. Simultaneously, as for the temperature of interior materials in the cabin, the temperature of the top surface of an instrument panel rises to nearly 100° C., and the temperature of the ceiling rises to nearly 70° C. Needless to say, it is unpleasant for occupants to get into the vehicle in such circumstances. Even when a ventilation or air-conditioning apparatus is activated, the temperature of the interior materials is not easily reduced, and radiation heat continues to be dissipated toward occupants for a long time. Accordingly, the comfort of the occupants is greatly impaired. One of causes of such an increase in temperature is intrusion of solar radiation into the cabin and intrusion of heat from a vehicle body panel which has absorbed the solar radiation into the cabin. Other causes include insufficient elimination or dissipation of heat accumulated in the cabin to the outside.
In order to suppress such an increase in temperature, measures to reduce the amount of intruding heat have hitherto been considered.
As a target for the above-described measures, first, the vehicle's glass is conceived. The transmittance of solar radiation into the cabin is reduced by adjusting the composition of glass so that the glass absorbs part of the solar radiation. Taking windshield glass as an example, the transmittance of solar radiation is reduced to, for example, 45% to 53% in existing vehicles. The amount of solar radiation coming into the cabin through the glass is thus reduced.
As another target for the above-described measures, next, an outer panel is conceived. In terms of heat transfer via an outer panel, there are cases of taking measures for the front surface of the outer panel, namely, a surface exposed to the solar radiation and taking measures for the back surface side of the outer panel. A coating material suppressing absorption of solar radiation in the front surface of the outer panel, which is publicly known, for example, in a construction field, does not satisfy application requirements in a field which requires high designability like the outer panel of the vehicle. On the contrary, as the measure for the back surface side of the outer panel, there have been known a measure focusing on a surface facing the back surface of the outer panel, namely, the back surface of the interior constituting a cabin, and a measure focusing on a back surface itself of the outer panel (see Japanese Patent Applications Laid-Open No. 2001-158306 and No. 2002-012094).